1. Field of the Invention
The present invention relates to handheld dehiders and powered skinning knives used to remove the hide of a carcass in a meat processing facility. More specifically, the present invention relates to dehiders that use a pair of cutting disks driven in opposed cutting oscillations.
2. Description of Related Art
Handheld dehiders are used in meat processing facilities to remove the hide from an animal carcass. The most common type of dehider includes a pair of adjacent cutting disks or blades that are driven in opposed cutting oscillations by a corresponding pair of pushrods. The basic design is shown in U.S. Pat. No. 5,122,092 assigned to Jarvis Products Corporation, the assignee of the present invention. Similar dehider designs are shown and described in U.S. Pat. Nos. 4,368,560, 3,435,522 and 2,751,680.
In the dehider design described in the patents above, each cutting blade includes teeth around its perimeter. The adjacent disk blades are driven in opposed cutting oscillations by a pair of pushrods connected to an eccentric drive mechanism operated by a pneumatic motor mounted in the handle of the tool.
The motor rotates a pinion gear, which turns a main drive gear oriented at ninety degrees to the axis of the motor. The main drive gear turns the eccentric shaft to oscillate the pushrods. During each oscillation, the teeth on one disk blade move past the teeth on the adjacent and oppositely moving disk blade. This produces a shearing and cutting action that quickly removes the hide from the carcass.
Although this dehider design has proven effective, existing designs tend to slow down under a heavy cutting load and then return to a higher speed as the cutting load is removed. To achieve the optimum cutting speed while operating under load, dehiders of this type must be set to run at a higher speed when they are not cutting. This higher no-load speed produces undesirable increases in tool wear and noise. The excess speed under the no-load condition is particularly problematical for a dehider having oscillating blades due to the frequent forward and back reversals of the blades and pushrods and the wear associated with the oscillating motion at high speed.
Another problem in existing designs lies in the design of the oscillating disk blades. These blades have heretofore been constructed with a constant thickness at all locations—except at the cutting edges where the thickness decreases to form the sharpened blade edges and teeth. In particular, the inner bearing area of the cutting disk has been of the same thickness as the outer portions of the blade. Each blade rotates about a bearing formed by a hole in this inner bearing area.
The limited thickness of the blade is advantageous at the outer edges of the blade, but it limits the bearing surface area at the center. The limited size of the bearing center hole produces wear at a greater rate than is desirable. As the blade wears, the center hole enlarges until the blade eventually becomes unusable. Often, it is this center bearing wear that limits the useful life of the blade. If not for this excess bearing wear, the blade could be sharpened additionally and the useful life of the blade extended.
Still another problem lies in the oscillating nature of the eccentric-driven pushrods and blades, which produces substantial vibration. A known method of reducing this vibration is to use a counterbalance mass on the main drive gear, however, this solution is only partly effective. In order to avoid interference with the oscillating pushrods, the main drive gear and any counterbalance mass connected thereto must be vertically offset from the plane of the pushrods. The offset between the moving mass of the pushrods and the oppositely moving mass of the counterbalance on the main drive gear produces a wobbling motion.
Initially, the magnitude of this wobbling motion is quite limited and the tool can be used comfortably for long periods of time. However, over time, the wobbling motion produces significant excess wear. As the bearings and moving parts begin to wear, the wobble increases in amplitude until it produces an extremely objectionable vibration. Moreover, the wear produced by this motion shortens the lifetime of the component parts in the tool.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a handheld dehider that operates at a nearly constant speed when operating under a load and when operating without a load.
Yet another object of the present invention is to provide a handheld dehider with blades that wear at the center bearing more slowly than existing designs.
A further object of the present invention is to provide a handheld dehider with less vibration that can be comfortably used for long periods of time.
It is another object of the present invention to provide a handheld dehider that wears less rapidly due to reduced vibration.
Still another object of the invention is to provide a counterbalanced eccentric shaft for a handheld dehider with an integrated counterbalance mass.
It is yet another object of the present invention to provide a counterbalance cup for a handheld dehider with an integrated counterbalance mass.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.